Wigner molecules in polygonal quantum dots: A density functional study

We investigate the properties of many-electron systems in two-dimensional polygonal (triangle, square, pentagon, hexagon) potential wells by using the density functional theory. The development of the ground state electronic structure as a function of the dot size is of particular interest. First we show that in the case of two electrons, the Wigner molecule formation agrees with the previous exact diagonalization studies. Then we present in detail how the spin symmetry breaks in polygonal geometries as the spin density functional theory is applied. In several cases with more than two electrons, we find a transition to the crystallized state, yielding coincidence with the number of density maxima and the electron number. We show that this transition density, which agrees reasonably well with previous estimations, is rather insensitive to both the shape of the dot and the electron number.Comment: 8 pages, 11 figure

Optical measurement of torque exerted on an elongated object by a non-circular laser beam

We have developed a scheme to measure the optical torque, exerted by a laser beam on a phase object, by measuring the orbital angular momentum of the transmitted beam. The experiment is a macroscopic simulation of a situation in optical tweezers, as orbital angular momentum has been widely used to apply torque to microscopic objects. A hologram designed to generate LG02 modes and a CCD camera are used to detect the orbital component of the beam. Experimental results agree with theoretical numerical calculations, and the strength of the orbital component suggest its usefulness in optical tweezers for micromanipulation.Comment: 6 pages, 7 figures, v2: minor typographical correction

Internal Migration and Regional Population Dynamics in Europe: Finland Case Study

Both natural increase and internal migration have played roles in the shaping of population distribution of Finland since 1900. Far reaching recent changes in the economy have brought about massive shift of jobs from agriculture to manufacturing and services. As a result people have relocated from rural to urban areas. Both natural change and net migration have distinct geographical patterns, resulting in serious depopulation in remote areas in the east and north of the country. Internal migration benefits the south, the west, coastal areas, urban agglomerations and suburban areas. International migration is a marginal phenomenon in Finland and has little impact on population dynamics. Net migration losses in the past were offset by high natural increase and in recent decades Finnish emigrants have returned. Urban concentration is a dominant feature of the Finnish migration system. At the subregional level, suburbanisation is visible, but is not as strong as in the overcrowded metropolises of Western Europe. The relationships between migration and size of municipality, migration and population density and migration and urban/rural class of municipalities show that the process of concentration is the strongest force at work in shifting people to urban agglomerations and their suburban rings. Regional patterns of migration show strong transfers of population from north and east to south and to lesser extent to west of the country. The Baltic Sea coast has a strong attraction to migrants. Migration is sex-selective, with a much higher propensity of females to leave remote and rural areas and migrate to urban centres and the southern part of the country. The result is a significant gender imbalance: a deficiency of females in rural areas and in the north and east of the country and a surplus in urban and semi-urban areas. However, the economic indicator unemployment has a rather weak and imprecise effect on migrants

Optical application and measurement of torque on microparticles of isotropic nonabsorbing material

We show how it is possible to controllably rotate or align microscopic particles of isotropic nonabsorbing material in a TEM00 Gaussian beam trap, with simultaneous measurement of the applied torque using purely optical means. This is a simple and general method of rotation, requiring only that the particle is elongated along one direction. Thus, this method can be used to rotate or align a wide range of naturally occurring particles. The ability to measure the applied torque enables the use of this method as a quantitative tool--the rotational equivalent of optical tweezers based force measurement. As well as being of particular value for the rotation of biological specimens, this method is also suitable for the development of optically-driven micromachines.Comment: 8 pages, 6 figure

A facility for investigation of multiple hadrons at cosmic-ray energies

An experimental arrangement for studying multiple hadrons produced in high-energy hadron-nucleus interactions is under construction at the university of Turku. The method of investigation is based on the detection of hadrons arriving simultaneously at sea level over an area of a few square meters. The apparatus consists of a hadron spectrometer with position-sensitive detectors in connection with a small air shower array. The position resolution using streamer tube detectors will be about 10 mm. Energy spectra of hadrons or groups of simultaneous hadrons produced at primary energies below 10 to the 16th power eV can be measured in the energy range 1 to 2000 GeV

Observations of cosmic-ray modulations in the fall, 1984

Modulation of cosmic-ray energy spectrum was studied by using the Turku double neutron monitor. The multiplicity region of detected neutrons produced by cosmic ray hadrons in the monitor was divided into seven categories corresponding to mean energies 0.1, 0.3, 1.0, 3.2, 8.6, 21, and 94 GeV of hadrons at sea level. Based on 24-hour frequencies, a statistical analysis showed that modulation of the intensity in all categories occurred during several periods in the fall 1984. The magnitude of the variation was a few per cent

Spectral analysis of the Forbush decrease of 13 July 1982

The maximum entropy method has been applied in the spectral analysis of high-energy cosmic-ray intensity during the large Forbush event of July 13, 1982. An oscillation with period of about 2 hours and amplitude of 1 to 3% was found to be present during the decrease phase. This oscillation can be related to a similar periodicity in the magnetospheric field. However, the variation was not observed at all neutron monitor stations. In the beginning of the recovery phase, the intensity oscillated with a period of about 10 hours and amplitude of 3%